This invention relates to a pulp molding die for molding pulp articles from used pulp and the like. Such pulp articles are suitably used as packaging and shock-absorbing materials, for example, egg boxes, fruit crates, packages for industrial products. This invention also relates to the method for molding such pulp articles.
Conventionally, in Japan, plastic and Styrofoam containers have mainly been used for packing industrial products, or the like. However, such containers add to environmental problems since they are not biodegradable, they release hazardous gas upon incineration, and so on. Therefore, conversion to fiber containers using old pulp, which can be reused many times, has come to be investigated.
The conventional pulp molding die consists of a main body and a wire mesh for the molding surface covering the main body. The wire mesh has a desired shape, which can be highly complex, of an article to be molded. The surface of the main body covered with the wire mesh also has complementary shape to the wire mesh. The main body is composed of aluminum blocks having numerous pores for water passage, and the blocks are joined together. The main body is joined to the wire mesh by connecting means such as bolts. The die may have a highly complex shape.
Washing the conventional molding die of the wire-mesh type using a shower of water at each interval of molding can prevent, to some extent, the water passage from becoming clogged. However, washing complexly shaped dies is extremely time consuming. Moreover, there are problems such as (1) the need for time, skill, and experience in the production of molding dies having complex shapes, (2) the difficulty in eliminating unwanted marks of the joints and patterns of the wire mesh from the surface of the final product, and (3) the inability to form letters or minute designs since the wire conventionally used cannot produce precise edges and corners. Further, when the pores for water passage are clogged, the operation has to be stopped and the molding die is washed by pressurized water.
Another type of a pulp molding die has been disclosed in Japanese Patent Laid-Open 60-9704. The die is composed of a single layer of particles forming the molding surface of a size chosen to provide a smooth surface. The particles, for example, made of ceramics, are bonded by a resin bonding agent, leaving pores. The thickness of this layer is 5-60 mm. There may be a backing plate (4 in FIG. 5); the specific example of this plate has a porosity of 7%.
However, this type of a die has some problems. In actual use, this mold (with the plate 4) may clog, because large areas of the porous molding layer are directly backed by unapertured areas of the plate. Thus the continuous production of the pulp articles is interrupted for a declogging procedure. Moreover, the die is prone to distortion during mass production, which requires the die to withstand repeated decompression, since the molding die is bonded only by the resin.
The present invention intends to solve the above-discussed conventional problems by providing a pulp molding die for molding pulp articles, which: (1) hardly experiences clogged pores, (2) can mold pulp articles having smooth surfaces, (3) is not prone to be damaged by repeated use, and (4) can be easily produced in a short amount of time. Moreover, the critical number of cycles in which molding a pulp article is continuously repeated without interruption can be greatly increased with the mold of the invention. The present invention is further intended to provide a pulp molding process, using the above-discussed pulp molding die, to greatly increase the critical number of possible continuous pulp moldings.